1. Field of the Invention
This invention relates to zoom lenses having a movable diaphragm, and more particularly to zoom lenses with a positive first lens component in the front of a varifocal lens system, and a diaphragm in the rear of the varifocal system arranged to move with the first lens component during a zooming operation.
2. Description of the Prior Art
A zoom lens in which a diaphragm is movable with another lens component when zooming is disclosed in U.S. Pat. No. 3,848,969.
This zoom lens is of the so-called two-component type. It includes a front component of negative power and a rear component of positive power with the air separation therebetween being changed to effect zooming. When zooming, the diaphragm is moved. In this lens, the air separation between the components is effectively utilized to achieve minimization of the bulk and size of the zoom lens.
In this type of zoom lens, however, a significant increase in the zoom ratio leads to a tendency to increase the bulk and size of the lens system. Therefore, the use of such an arrangement in high range zoom lens is not very desirable.
In two-component zoom lenses, it is usual to arrange the diaphragm either at an intermediate point in the space between the negative first and positive second components, or in a space within the second component. On the other hand, in order to allow the diaphragm to be stationary during zooming, its mechanical interference with the adjacent components may be avoided by providing for a sufficient air space. When the diaphragm is positioned between the front and rear parts of the second component the operating mechanism must be constructed so as to impart the same movement to the front and rear parts. This tends to wastefully increase the air space and make the structure unduly complicated.
Another type of zoom lens is the so-called four-component type. It includes from front to rear, a first component for focusing, second and third components for zooming, and an image forming or fourth component. Generally, its diaphragm is arranged just to the rear of the third component and is stationary during zooming. Such a lens is disclosed, for example, in U.S. Pat. No. 3,970,367. The four-component zoom lens has a longer distance between the diaphragm and the image plane than the two-component zoom lens. This leads to a tendency to increase the necessary number of mechanical members in the signal transmission from the interior of a camera housing to the diaphragm and the complexity of the transmission. However, the bulk and size of the zoom lens system can be reduced to some extent by moving the diaphragm during zooming. Nevertheless, with the four-component type, similar to the two-component type zoom lens, when the range of variation of the image magnification of the zoom lens is substantially increased, a rapid increase in the bulk and size of the lens system results.